Semiconductor device and method of manufacturing the same

ABSTRACT

A first semiconductor chip is produced by affixing a thermo-compression sheet to the back surface of a wafer having a circuit formed on its front surface. The first semiconductor chip is mounted on a circuit board including an insulating substrate and a wiring layer provided on the insulating substrate so that the back surface of the first semiconductor chip faces the circuit board. A second semiconductor chip produced in the same manner as the first semiconductor chip is mounted on the first semiconductor chip with its back surface facing the first semiconductor chip. Each of the first and second semiconductor chips is wire-bonded to the wiring layer with a wire. The first and second semiconductor chips and the wire are sealed with a sealing resin. The wiring layer is connected to external connection terminals through via holes provided in the insulating substrate.

This is a divisional of application Ser. No. 09/223,272, filed Dec. 30,1998, the entire content of which is hereby incorporated by reference inthis application now U.S. Pat. No. 6,100,594.

FIELD OF THE INVENTION

The present invention relates to a semiconductor device and a method ofmanufacturing the same, and more particularly relates to a semiconductordevice having a structure substantially miniaturized to a chip size,i.e., a CSP (Chip Size Package) structure, and a method of manufacturingsuch a semiconductor device.

BACKGROUND OF THE INVENTION

Miniaturization of a semiconductor device is in progress so as toachieve a high-density semiconductor device for use on a printed circuitboard. Recently, a semiconductor device substantially miniaturized to achip size has been developed. The structure of such a miniaturizedsemiconductor device is called a CSP structure. Japanese Publication ofUnexamined Patent Application No. 121002/1997 (Tokukaihei 9-121002)discloses a semiconductor device having the CSP structure shown in FIG.13(a). This semiconductor device includes a semiconductor chip 42disposed with its circuit formed surface facing up, and wires 43 forelectrically connecting the semiconductor chip 42 to a wiring pattern47. The above publication discloses another semiconductor device havingthe CSP structure shown in FIG. 13(b). This semiconductor deviceincludes a semiconductor chip 64 disposed with its circuit formedsurface facing down, and a bump electrode 70 for electrically connectingthe semiconductor chip 64 to a wiring pattern 66.

In FIG. 13(a), 41 is a wiring component, 42 is a semiconductor chip, 43is a wire, 44 is a resin sealing member, 45 is a throughhole, 46 is asubstrate, 47 is a wiring pattern, 48 is an insulating material, 49 isan external connection-use terminal, 50 is an external connection area,51 is an electrode, 52 is a window opening section, and 53 is an innerconnection area. In FIG. 13(b), 61 is a throughhole, 62 is a wiringcomponent, 63 is an electrode, 64 is a semiconductor chip, 65 is a resinsealing member, 66 is a wiring pattern, 67 is an inner connection area,68 is an external connection area, 69 is an external connection-useterminal, and 70 is a bump electrode.

In some devices such as portable devices, a plurality of semiconductorchips are mounted in a package so as to increase the added value andcapacity of memory, etc. For example, a multi-chip module is providedwith a plurality of semiconductor chips arranged parallel to each otherin a package. However, such an arrangement makes it impossible toproduce a package smaller than the total area of the semiconductor chipsto be mounted. In order to solve the problem, a stacked packageincluding a plurality of semiconductor chips laminated in a package toachieve a high packaging density is disclosed in Japanese Publication ofUnexamined Patent Application No. 90486/1993 (Tokukaihei 5-90486).

Specifically, the semiconductor devices disclosed in the abovepublication are each packaged in ceramic packages and arranged in thefollowing manner. In one of the semiconductor devices, a pair ofsemiconductor chips are adhered to each other with their back surfaceswhere a circuit is not formed facing each other, and are mounted onanother pair of semiconductor chips via metal bumps. In the othersemiconductor device, a pair of semiconductor chips are adhered to eachother with the circuit formed surface of one semiconductor chip facingthe back surface of the other semiconductor chip.

The above-mentioned stacked package is a small, high-densitysemiconductor device. However, a semiconductor device smaller than sucha stacked package has been required. For that reason, a semiconductordevice having a CSP structure as well as a stacked package structure isrequired to be produced.

In a semiconductor device having a CSP structure where the semiconductorchips are laminated, an adhesive agent (paste) potting method and amethod using a thermo-compression sheet are utilized for bonding thesemiconductor chip to the substrate, and for bonding the laminatedsemiconductor chips to each other.

In the potting method, if the amount of the adhesive agent is excessive,a large amount of adhesive agent spreads beyond the outer edge of thesemiconductor chip. For example, as shown in FIG. 14(a), when bondingsemiconductor chips 81 and 82 to each other with their back surfacesfacing each other, an adhesive agent 87 between the semiconductor chips81 and 82 overflows. In addition, as shown in FIG. 15, in the step ofwire-bonding the semiconductor chip 82 disposed on the top to anelectrode section of a wiring layer 84 (before a sealing resin 89 andpackaging-use external terminals 90 are formed), wiring on an insulatingsubstrate 83 must be provided far from the side surfaces of thesemiconductor chips 81 and 82 so as to keep the overflown adhesive agent87 a from coming into contact with a jig 92 of a wire bonder. Such anarrangement causes the package size to be increased in the end.Furthermore, as shown in FIG. 14(b), when bonding the back surface ofthe semiconductor chip 82 to the circuit formed surface of thesemiconductor chip 81, the overflown adhesive agent 87 a may stick to anelectrode pad provided on the semiconductor chip 81.

On the other hand, if the amount of the adhesive agent is too small, agap is produced between the semiconductor chips 81 and 82. This gapcannot be filled with the sealing resin 89, thereby causing problemssuch as separation of the semiconductor chip 82 from the semiconductorchip 81.

The method using a thermo-compression sheet requires the steps ofplacing members at the right locations. Specifically, athermo-compression sheet having the same size as the semiconductor chip82 must be placed accurately at a specific location an the semiconductorchip 81. In addition, the semiconductor chip 82 must be bonded to thethermo-compression sheet so as to be located exactly on the top of thethermo-compression sheet.

In FIGS. 14(a) and 14(b), 85 is an insulating sheet, 86 is a metal bump,and 91 is an adhesive sheet.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a further-miniaturizedsemiconductor device having a stacked package structure as well as a CSPstructure.

In order to achieve the above object, a semiconductor device inaccordance with the present invention has a stacked package structureand a chip size package structure and is characterized in including:

an insulating substrate including a wiring layer having electrodesections;

a first semiconductor chip having a first insulating adhesion layeradhered to its back surface where a circuit is not formed, the firstsemiconductor chip being mounted on the wiring layer through the firstinsulating adhesion layer; and

a second semiconductor chip having a second insulating adhesion layeradhered to its back surface where a circuit is not formed, the secondsemiconductor chip being mounted on a circuit-formed front surface ofthe first semiconductor chip through the second insulating adhesionlayer;

each of the first and second semiconductor chips being wire-bonded tothe electrode section with a wire, the first and second semiconductorchips and the wire being sealed with a resin.

In the above structure, the first semiconductor chip and the secondsemiconductor chip are each wire-bonded to the electrode sectionprovided on the wiring layer with the wires, and the second insulatingadhesion layer is used for affixing the second semiconductor chip to thefirst semiconductor chip. This structure eliminates the need forwire-bonding the first and second semiconductor chips to points on thewiring layer, far from the side surfaces of the first and secondsemiconductor chips, considering a situation in which the excessivelyapplied adhesive agent overflows the space between the first and secondsemiconductor chips. Therefore, a miniaturized, high-densitysemiconductor device can be realized.

Furthermore, in the case of using a thermo-compression sheet, whenmounting the first or second semiconductor chip at a desired location,accurate positioning is required twice, i.e., positioning thethermo-compression sheet, etc., and positioning the first or secondsemiconductor chip on the thermo-compression sheet. In contrast, thefirst and second insulating adhesion layers according to the presentinvention are in advance disposed on the back surfaces of the first andsecond semiconductor chips, respectively. Therefore, the first or secondsemiconductor chip can be mounted at a desired location by accuratelypositioning it once. It is thus possible to miniaturize thesemiconductor device without complicating its manufacturing process.

A semiconductor device in accordance with the present invention can bearranged to include:

an insulating substrate including a wiring layer having electrodesections;

a first semiconductor chip having a circuit formed on its front surfaceand an insulating adhesion layer adhered to its back surface;

a metal bump , disposed between the first semiconductor chip and thewiring layer, for bump-bonding the front surface of the firstsemiconductor chip to the wiring layer so that the front surface facesthe wiring layer; and

a second semiconductor chip whose back surface where a circuit is notformed is mounted on the back surface of the first semiconductor chipthrough the insulating adhesion layer;

the second semiconductor chip being wire-bonded to the electrode sectionof the wiring layer with a wire, the first and second semiconductorchips and the wire being sealed with a resin.

In the above arrangement, the first semiconductor chip is connected tothe wiring layer through the metal bump, the second semiconductor chipis wire-bonded to the electrode sections on the wiring layer with wires,and the back surfaces of the first and second semiconductor chips areadhered to each other by the insulating layer. This arrangementeliminates the need for wire-bonding the second semiconductor chip topoints on the wiring layer, far from the side surfaces of the first andsecond semiconductor chips, considering a situation in which theexcessively applied adhesive agent overflows the space between the firstand second semiconductor chips. Therefore, a miniaturized, high-densitysemiconductor device can be realized.

In the case of using the thermo-compression sheet, when mounting thesecond semiconductor chip on the first semiconductor chip, accuratepositioning is required twice in a conventional manufacturing method,i.e., positioning the thermo-compression sheet on the firstsemiconductor chip, and positioning the second semiconductor chip on thethermo-compression sheet. However, the insulating adhesion layeraccording to the present invention are disposed on the back surface ofthe second semiconductor chip in advance. Therefore, the secondsemiconductor chip can be mounted at a desired location on the firstsemiconductor chip by accurately positioning it once. It is thuspossible to miniaturize the semiconductor chip without complicating itsmanufacturing process.

A method of manufacturing a semiconductor device in accordance with thepresent invention includes the steps of:

(a) forming a first insulating adhesion layer on a back surface of afirst wafer having a circuit formed on its front surface;

(b) producing separate first semiconductor chips from the first wafer bydicing;

(c) mounting the first semiconductor chip on a wiring layer with itsback surface facing the wiring layer;

(d) forming a second insulating adhesion layer on a back surface of asecond wafer having a circuit formed on its front surface;

(e) producing separate second semiconductor chips from the second waferby dicing;

(f) mounting the second semiconductor chip on the first semiconductorchip with its back surface facing the first semiconductor chip;

(g) wire-bonding the first semiconductor chip to an electrode section ofthe wiring layer with a wire;

(h) wire-bonding the second semiconductor chip to an electrode sectionof the wiring layer with a wire; and

(i) sealing the first and semiconductor chips and the wires.

With the above manufacturing method, since the first or secondsemiconductor chip has the first or second insulating adhesion layeradhered to its back surface in advance when being in the wafer state,the first or second semiconductor chip can be mounted at a desiredlocation without the step of accurately positioning the first or secondinsulating adhesion layer on the first or second semiconductor chip. Itis thus possible to simplify the process of manufacturing thesemiconductor chip.

Morever, in the above manufacturing method, the adhesive agent does notoverflow the space between the first and second semiconductor chips, thefirst and second semiconductor chips can be wire-bonded to the wiringlayer at a location closer to the edges of the first and secondsemiconductor chips. It is thus possible to realize a miniaturized,high-density semiconductor device.

A method of manufacturing a semiconductor device in accordance with thepresent invention including the steps of:

(a) forming an insulating layer and a metal bump on a wiring layer;

(b) mounting a first semiconductor chip on the wiring layer with itscircuit-formed surface facing the wiring layer;

(c) forming an insulating adhesion layer on a back surface of a waferhaving a circuit formed on its front surface;

(d) producing separate second semiconductor chips from the wafer bydicing;

(e) mounting the second semiconductor chip on the first semiconductorchip with its back surface facing the first semiconductor chip;

(f) wire-bonding the second semiconductor chip to the wiring layer witha wire; and

(g) sealing the first and second semiconductor chips and the wire.

In this manufacturing method, like the above-mentioned method of thepresent invention, since the second semiconductor chip has theinsulating adhesion layer adhered to its back surface in advance whenbeing in the wafer state, the second semiconductor chip can be mountedat a desired location without the step of accurately positioning theinsulating adhesion layer on the second semiconductor chip. It is thuspossible to simplify the process of manufacturing the semiconductorchip.

Furthermore, in the above manufacturing method, the adhesive agent doesnot overflow the space between the first and second semiconductor chips,the second semiconductor chip can be wire-bonded to the wiring layer ata location closer to the edges of the first and second semiconductorchips. It is thus possible to realize a miniaturized, high-densitysemiconductor device.

For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a semiconductor device in accordancewith the first embodiment of the present invention.

FIG. 2(a) is a plan view of a circuit board before being cut, and

FIG. 2(b) is a partially enlarged view of the circuit board shown inFIG. 2(a).

FIG. 3(a) is an explanatory view showing an arrangement of ball-likeexternal connection-use terminals, and

FIG. 3(b) is an explanatory view showing an arrangement of trapezoidalexternal connection-use terminals.

FIG. 4 is an explanatory view showing how laminated semiconductor chipsare each wire-bonded to the circuit board.

FIGS. 5(a) to 5(g) show one example of a process for manufacturing thesemiconductor device.

FIG. 6(a) is a partially enlarged view of the circuit board including awiring layer disposed on one surface of an insulating substrate, andFIG. 6(b) is a partially enlarged view of a circuit board including awiring layer disposed on each surface of the insulating substrate.

FIG. 7(a) is an explanatory view showing a wiring state when twolaminated semiconductor chips are connected to the same electrodesection, and

FIG. 7(b) is an explanatory view showing another state that the twolaminated semiconductor chips are connected to the same electrodesection.

FIG. 8(a) is an explanatory view showing a wiring state that the twolaminated semiconductor chips are connected to different electrodesections, and

FIG. 8(b) is an explanatory view showing another wiring state that thetwo laminated semiconductor chips are connected to different electrodesections.

FIG. 9(a) is an explanatory view showing one example of an arrangementof dummy pads formed on a first semiconductor chip, and

FIG. 9(b) is an explanatory view showing another example of thearrangement of the dummy pads disposed on the first semiconductor chip.

FIG. 10 is a cross-sectional view of a semiconductor device inaccordance with the second embodiment of the present invention.

FIGS. 11(a) to 11(g) show one example of a process for manufacturing thesemiconductor device.

FIG. 12(a) is a perspective view showing that a second semiconductorchip in the semiconductor device in accordance with the first embodimentor the second embodiment protrudes from a first semiconductor chip, and

FIG. 12(b) is a perspective view showing that the second semiconductorchip is reinforced.

FIG. 13(a) is a cross-sectional view showing a semiconductor devicehaving a CSP structure manufactured by a conventional wire bondingmethod, and

FIG. 13(b) is a cross-sectional view showing a semiconductor devicehaving a CSP structure manufactured by a conventional face-down bondingmethod.

FIG. 14(a) and FIG. 14(b) are cross-sectional views of conventionalsemiconductor devices having a stacked package structure.

FIG. 15 is a cross-sectional view of the semiconductor device shown inFIG. 14(a) during manufacturing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

The following descriptions will explain one embodiment of the presentinvention with reference to FIGS. 1 to 9.

As shown in FIG. 1, in a semiconductor device according to thisembodiment, a first semiconductor chip 1 and a second semiconductor chip2 are laminated in this order on a circuit board 5 including aninsulating substrate 3 and a wiring layer 4 mounted on the insulatingsubstrate 3. Regarding the first semiconductor chip 1 and the secondsemiconductor chip 2, the surface (front surface) on which an element isformed is hereinafter referred to as a “circuit formed surface”, and thesurface opposite thereto is referred to as a “back surface”.

The semiconductor chip 1 is disposed with its back surface facing theinsulating substrate 3. The second semiconductor chip 2 is mounted onthe circuit formed surface of the first semiconductor chip 1 through athermo-compression sheet (adhesion layer) 6 so that its back surface isadhered to the thermo-compression sheet 6.

The semiconductor device in accordance with the present embodiment isarranged so that the second semiconductor chip 2 is mounted on thecircuit formed surface of the first semiconductor chip 1. With thisarrangement, the second semiconductor chip 2 on the top of the firstsemiconductor chip 1 does not influence (interfere with) electrode padsof the first semiconductor chip 1. The circuit formed surface of thefirst semiconductor chip 1 is in advance coated with aninsulating-resin, etc. Namely, the coating is applied to the circuitformed surface of the first semiconductor chip 1 by a spin coatingmethod, etc. when the first semiconductor chip 1 is in a wafer statebefore subjected to dicing. In this case, the coating material on theelectrode pads (not shown) disposed on the circuit formed surface of thefirst semiconductor chip 1 is removed.

The first semiconductor chip 1 and the second semiconductor chip 2 areeach connected (wire-bonded) to electrode sections of the wiring layer 4on the insulating substrate 3 with wires 7.

The first semiconductor chip 1, the second semiconductor chip 2 and thewires 7, arranged as above, are covered by a sealing resin 8.

The insulating substrate 3 includes via holes 9 at the locationscorresponding to below-described land sections 12 constituting thewiring layer 4. Ball-like packaging-use external terminals 10 areconnected in an area-array-like arrangement to the land sections 12through the via holes 9 from the side of the insulating substrate 3, onwhich side the first semiconductor chip 1 and the second semiconductorchip 2 are not formed.

Next, the following descriptions will explain in further detail theabove-mentioned members constituting the semiconductor device inaccordance with the present embodiment.

FIG. 2(a) is a plan view of the circuit board 5 before being cut in theprocess of manufacturing the semiconductor device. As shown in FIG. 2(a)four guide holes 11 are formed in both side sections of the insulatingsubstrate 3 (the upper part and the lower part of the insulatingsubstrate 3 in FIG. 2(a)) of the circuit board 5 before being cut. Theguide holes 11 a formed in one of the side section and the guide holes11 b formed in the other side section have different shapes. These guideholes 11 are used for transporting the semiconductor device during itsmanufacturing process.

The material of the insulating substrate 3 is not particularly limited,and a resin substrate or a film having excellent heat resistance isacceptable. The insulating material 3 may be a resin substrate, etc.made of, for example, polyimide, epoxy resin containing glass fiber,bismaleid triazine (BT) resin, polyester, polyamide, fluororesin,ceramic, and polyester containing glass fiber. Polyimide is the mostpreferable of the above materials.

FIG. 2(b) is a partially enlarged view of the circuit board 5 shown inFIG. 2(a), showing the structure of the wiring layer 4. As shown in FIG.2(b), the wiring layer 4 includes the land sections 12, electrodesections 13, and wiring sections 14, disposed on the insulatingsubstrate 3. Each of the. wiring sections 14 connects the land section12 to the electrode section 13.

The electrode sections 13 are formed on both ends of the wiring layer 4(the left part and the right part of the wiring layer 4 in FIG. 2(b)).As explained in detail later, each of the electrode section 13 isconnected to the first semiconductor chip 1 or the second semiconductorchip 2 by the wire 7. Therefore, the electrode sections 13 are locatedoutside the area of the wiring layer 4, where the first semiconductorchip 1 and the second semiconductor chip 2 are mounted.

The land section 12 is a packaging-use external terminal forming sectionfor connecting the packaging-use external terminal 10 and the wiringlayer 4 through the via hole 9 of the insulating substrate 3.

The first semiconductor chip 1 can be completely insulated from thewiring layer 4 by, for example, providing a sheet of an insulating resinon an area of the wiring layer 4 where the first semiconductor chip 1 isto be mounted or applying an insulating resin coating to the area of thewiring layer 4. The wiring layer 4 is made of copper (Cu), aluminum(Al), gold (Au), nickel (Ni), and other materials. Cu is particularlypreferable because it is less costly. Methods of forming the wiringlayer 4 on the insulating substrate 3 include a vapor deposition methodand a plating method. In order to pattern the wiring layer 4 to form adesired pattern, a conventional photolithography method can be utilized.

FIG. 3(a) is a view seen from the back side of the semiconductor deviceshown in FIG. 1, i.e., the side where the packaging-use externalterminals 10 are disposed. As shown in FIG. 3(a), ball-likepackaging-use external terminals 10 are disposed in an area-array-likearrangement, and connected to the land sections 12 provided on thewiring layer 4. The packaging-use external terminals 10 are not limitedto a ball-like shape, and may have a trapezoidal shape as shown in FIG.3(b).

Each of the wires 7 is used for connecting the electrode pad disposed onthe first semiconductor chip 1 or the second semiconductor chip 2 to theelectrode section 13 of the wiring layer 4. In a conventionalsemiconductor device, a gold ball provided on only one end of the wireis in contact with the electrode pad of the first semiconductor chip orthe second semiconductor chip, and the other end of the wire isconnected to the electrode section of the wiring layer on the insulatingsubstrate. Here, the gold ball can be provided on only one end of thewire. The gold ball is brought into contact with the electrode pad byimposing a load lighter than the load applied in connecting, bythermo-compression bonding, the wire to the electrode section of thewiring layer on the insulating substrate. This is because connecting thewires to the semiconductor chips by thermo-compression bonding, i.e., byapplication of a heavy load, increases the possibility of damaging thesemiconductor chips.

However, the above conventional arrangement has the following problem.Namely, the wires, especially those connected to the secondsemiconductor chip, are connected to the electrode sections of thewiring layer provided on the circuit board at a small angle with respectto the circuit board. Therefore, the wire is connected to the circuitboard, far from the end of the first semiconductor chip.

In order to solve the problem, in the semiconductor device according tothe present embodiment, the first semiconductor chip 1 and the secondsemiconductor chip 2 are each wire-bonded to the circuit board 5 asshown in FIG. 4. The first semiconductor chip 1 and the circuit board 5are wire-bonded in the same manner as the conventional semiconductordevice. Then, the wire 7 is connected to the circuit board 5 with a goldball 7 a provided on one end of the wire 7. Thereafter, the other end ofthe wire 7 is connected, by thermo-compression bonding, to a gold bump16 formed on the electrode pad of the second semiconductor chip 2 inadvance so as to connect the second semiconductor chip 2 to the circuitboard 5.

Since wire-bonding between the second semiconductor chip 2 and thecircuit board 5 is performed as above, the wire 7 connected to thesecond semiconductor chip 2 is connected to the circuit board 5 at anangle closer to 90° with respect to the circuit board 5. Therefore , thewire 7 is connected to the circuit board 5 at a closer location to theend of the first semiconductor chip 1, thereby enabling furtherminiaturization of the semiconductor device in accordance with thepresent embodiment.

The wire 7 is connected to the gold bump 16 by thermo-compressionbonding by a load nearly equal to the load applied when connecting thewire 7 to the electrode section of the wiring layer 4 on the insulatingsubstrate 3 by thermo-compression bonding. However, by using the goldbump 16, the stress applied to the second semiconductor chip 2 can belowered. It is thus possible to reduce the possibility that the secondsemiconductor chip 2 is damaged by a heavy load applied there to.

The gold bump 16 is formed by connecting a gold ball, provided on theend of the wire by the conventional method, to the electrode pad on thesecond semiconductor chip 2, and then cutting the wire 7. Thereafter, bymaking the upper surface of the gold bump 16 flat with a stamping jig,the wire 7 can be surely affixed to the gold bump 16 bythermo-compression bonding.

Note that the first semiconductor chip 1 and the circuit board 5 can bewire-bonded to each other in the same manner as the above-mentionedwire-bonding of the second semiconductor chip 2 and the circuit board 5.

The following descriptions will explain one example of the process(including steps (1) to (5)) for manufacturing the semiconductor devicein accordance with the present embodiment with reference to FIGS. 5(a)to 5(g).

(1) First, the first semiconductor chip 1 is mounted on the circuitboard 5 (see FIG. 5(a)) When the first semiconductor chip 1 is in awafer state, the insulating thermo-compression sheet 6 is adhered to theback surface of the wafer. Then, the wafer is cut to produce separatepieces of first semiconductor chips 1. The first semiconductor chip 1 ismounted on the circuit board 5 at a location inside a mount locationrecognition-use mark 15 provided on the circuit board 5. Here, insteadof providing the thermo-compression sheet 6 in advance when the firstsemiconductor chip 1 is in the wafer state, an insulating paste made ofepoxy resins, etc. may be applied onto the circuit board 5 before thefirst semiconductor chip 1 is mounted on the circuit board 5.

(2) Next, the second semiconductor chip 2 is mounted on the circuitformed surface of the first semiconductor chip 1 (see FIG. 5(b)). Whenthe second semiconductor chip 2 is in the wafer state, the insulatingthermo-compression sheet 6 is adhered to the back surface of the wafer,and then the wafer is cut to produce separate pieces of secondsemiconductor chips 2. The second semiconductor chip 2 is accuratelypositioned at a specific location on the circuit formed surface of thefirst semiconductor chip 1.

By affixing the thermo-compression sheet 6 to the back surface of thesecond semiconductor chip 2 in advance, accurate positioning isnecessary only when mounting the second semiconductor chip 2 on thefirst semiconductor chip 1. Therefore, since one step requiring accuratepositioning is omitted in the process for manufacturing thesemiconductor device in accordance with the present embodiment, thismanufacturing process is simplified compared with the conventionalprocess in which the thermo-compression sheet 6 is disposed on thecircuit formed surface of the first semiconductor chip 1, and then thesecond semiconductor chip 2 is adhered to the thermo-compression sheet6.

(3) Then, each of the electrode pads (not shown) disposed on the firstsemiconductor chip 1 and the second semiconductor chip 2 is connected,with the wire 7 made of Au, to the electrode section 13 formed in thewiring layer 4 on the circuit board 5. More specifically, the firstsemiconductor chip 1 and the wiring layer 4 are first electricallyconnected to each other (see FIG. 5(c)), and then the secondsemiconductor chip 2 and the wiring layer 4 are electrically connectedto each other (see FIG. 5(d)). Since the first semiconductor chip 1 andthe second semiconductor chip 2 are each electrically connected to thewiring layer 4 in the above order, it is possible to avoid such aproblem that the wire 7 for connecting the first semiconductor chip 1 tothe circuit board 5 and the wire 7 for connecting the secondsemiconductor chip 2 to the circuit board 5 cross each other, andprevent connection of the firs t semiconductor chip 1 to the circuitboard 5.

(4) Thereafter, each of the packaging-use external terminals 10 isdisposed on the location where the via hole 9 is provided on theinsulating substrate 3 on the circuit board 5 (see FIG. 5(f)). Here,positioning the packaging-use external terminal 10 is performed in sucha manner that a solder ball is temporarily fixed to each via hole 9,heated in a reflow furnace, and then joined to the land section 12.Methods of temporarily fixing the solder ball to the via hole 9 includea method in which the solder ball is affixed to the via hole 9 afterapplying a flux to the via hole 9, and a method in which the solder ballis affixed to the via hole 9 after adhering the flux to the solder ball.

(5) Finally, a plurality of semiconductor devices produced on thecircuit board 5 are divided into pieces of semiconductor devices (seeFIG. 5(d)) by cutting the insulating substrate 3 along its unnecessarypart, i.e., along the outer edge of the sealing resin 8 of eachsemiconductor device. Methods of cutting the insulating substrate 3include a punching method using die, and an eximer laser cutting method.

As shown in FIG. 6(a), the semiconductor device in accordance with thepresent embodiment includes the wiring layer 4 on only one of thesurfaces of the insulating substrate 3. However, the wiring layer 4 canbe provided on both surfaces of the insulating substrate 3 as shown inFIG. 6(b).

When the wiring layer 4 is formed on both surfaces of the insulatingsubstrate 3, as shown in FIG. 6(b) the wiring layers 4 on the respectivesurfaces are electrically connected to each other through the plated viaholes 9 as shown in FIG. 6(b) Regarding the wiring layer 4 on the sideof the insulating substrate 3, the side where the first semiconductorchip 1 is not mounted, the area where the packaging-use externalterminals 10 are not to be formed are covered with a solder resist 20,etc. In the area which is not covered with the solder resist 20, i.e.,the area where the packaging-use external terminals 10 are to beprovided, the packaging-use external terminals 10 are arranged in anarea-array-like pattern.

When connecting the first semiconductor chip 1 and the secondsemiconductor chip 2 to the electrode sections 13 of the wiring layer 4with the wires 7, if the wires 7 become too close to each other becauseof the layout of the electrode pads of the first semiconductor chip 1and the second semiconductor chip 2, the wires 7 can be arranged asbelow.

When connecting the first semiconductor chip 1 and the secondsemiconductor chip 2 to the same electrode section 13 of the wiringlayer 4, two arrangements shown in FIGS. 7(a) and 7(b) are acceptable.In the arrangement shown in FIG. 7(a), the electrode section 13 of thewiring layer 4, to which two wires 7 are connected, is arranged to havetwo parts. In the arrangement shown in FIG. 7(b), an electrode pad 17 aof the first semiconductor chip 1 is connected to an electrode pad 17 bof the second semiconductor chip 2 with the wire 7, and the electrodepad 17 a is connected to the electrode section 13 of the wiring layer 4with the wire 7, thereby connecting each of the electrode pads 17 a and17 b to the electrode section 13.

When connecting the first semiconductor chip 1 and the secondsemiconductor chip 2 to different electrode sections 13 of the wiringlayer 4, two arrangements shown in FIGS. 8(a) and 8(b) are acceptable.In the arrangement shown in FIG. 8(a), the electrode pad 17 a of thefirst semiconductor chip 1 and the electrode pad 17 b of the secondsemiconductor chip 2 are each connected directly to the electrodesection 13 of the wiring layer 4 with the wire 7. In the arrangementshown in FIG. 8(b), dummy pads 18 are provided on the firstsemiconductor chip 1, and the electrode pad 17 b disposed on the secondsemiconductor chip 2 is connected to the electrode section 13 of thewiring layer 4 via the dummy pad 18. This arrangement shown in FIG. 8(b)is more preferable because the overhanging part of the wire 7 is shorterthan that in the arrangement shown in FIG. 8(a).

FIGS. 9(a) and 9(b) s how examples of the arrangement of the dummy pads18 provided on the first semiconductor chip 1.

Embodiment 2

With reference to FIGS. 10 to 12, the following descriptions willexplain the second embodiment of the present invention. The membershaving the same structure as those in the above-mentioned firstembodiment will be designated by the same reference numbers and theirdescription will be omitted.

A semiconductor device in accordance with the present embodiment isarranged as shown in FIG. 10. Specifically, a first semiconductor chip21 is mounted on a circuit board 5 with its circuit formed surfacefacing the circuit board 5, i.e., facing down. The circuit board 5includes an insulating substrate 3, and a wiring layer 4 formed on theinsulating substrate 3. A second semiconductor chip 22 is mounted on theback surface of the first semiconductor chip 21 through athermo-compression sheet 6. The back surf ace of the secondsemiconductor chip 22 faces the first semiconductor chip 21. Namely, theback surfaces of the first semiconductor chip 21 and the secondsemiconductor chip 22 are adhered to each other through thethermo-compression sheet 6. The thermo-compression sheet 6 is providedas an adhesion layer for holding the second semiconductor chip 22 on thefirst semiconductor chip 21.

The first semiconductor chip 21 is electrically connected to firstelectrode sections (not shown) provided in the wiring layer 4 throughmetal bumps 23. The first electrode sections are disposed inside an areaof the wiring layer 4, where the first semiconductor chip 21 is mounted.

Meanwhile, the second semiconductor chip 22 is electrically connected tosecond electrode sections (not shown) provided in the wiring layer 4with wires 7. Since the second electrode sections are used forwire-bonding the second semiconductor chip 22 to the wiring layer 4,they are disposed outside the area of the wiring layer 4, where thefirst semiconductor chip 21 and the second semiconductor chip 22 aremounted.

A resin sheet 24 is provided between the first semiconductor chip 21 andthe wiring layer 4. The resin sheet 24 is formed by extending a resinsheet used in the step of connecting the first semiconductor chip 21 tothe wiring layer 4 through the metal bumps 23.

If electrode pads provided on the circuit formed surface of the firstsemiconductor chip 21 are made of Al, the metal bumps 23 are preferablymade of Au which is easily alloyed with Al. With this arrangement, themetal bumps 23 can be more firmly affixed to the electrode pads.

The material for forming the resin sheet 24 may be a thermoplastic resinor a thermosetting resin. However, the thermoplastic resin is morefavorable than the thermosetting resin because the resin sheet 24 isused for the following purpose. Namely, it is used so that the resinextends by heat applied in connecting the first semiconductor chip 21 tothe wiring layer 4 with the metal bumps 23, covers the metal bumps 23 asjunctions, and prevents degradation of the junctions caused by shock,etc.

The resin sheet 24 can be a three-layer resin sheet including a layer ofa light blocking material such as metallic foil. With this arrangementit is possible to prevent a malfunction of the first semiconductor chip21 due to a light incident from the surface where the packaging-useexternal terminals 10 are mounted passing through the semiconductordevice. In this case, the size of the metallic foil must be such thatthe metallic foil is out of contact with the metal bumps 23.

Although the semiconductor device in accordance with the presentembodiment uses the resin sheet 24, the following arrangement is alsoacceptable. Namely, the semiconductor chip 21 is mounted without usingthe resin sheet 24, and then the space produced at a junction of thefirst semiconductor chip 21 and the wiring layer 4 is filled with aliquid resin, etc., thereby covering the metal bumps 23 as thejunctions.

Next, referring to FIGS. 11(a) to 11(g), the following descriptions willexplain the process (including steps (1) to (7)) for manufacturing thesemiconductor device in accordance with the present embodiment.

(1) First, the resin sheet 24 and the metal bumps 23 are disposed on thecircuit board 5 (see FIG. 11(a)). In this case, each of the metal bumps23 is disposed on the first electrode section provided in the wiringlayer 4 on the circuit board 5. The resin sheet 24 is disposed on thecircuit board 5 at the location where the first semiconductor chip 21and the second semiconductor chip 22 are to be mounted.

(2) Next, the first semiconductor chip 21 is connected to the wiringlayer 4 on the circuit board 5 by a flip chip method in a face-down mode(see FIG. 11(b)).

(3) Then, the second semiconductor chip 22 is mounted on the backsurface of the first semiconductor chip 21 (see FIG. 11(c)). When thesecond semiconductor chip 22 is in a state of wafer, the insulatingthermo-compression sheet 6 is adhered to the back surface of the wafer,and then the wafer is cut to produce chips, i.e., separate pieces ofsecond semiconductor chips 22. The second semiconductor chip 22 isaccurately positioned at a specific location on the circuit formedsurface of the first semiconductor chip 21.

Like the manufacturing process described in the first embodiment, theprocess for manufacturing the semiconductor device in accordance withthe present embodiment is simplified by adhering the thermo-compressionsheet 6 to the back surface of the second semiconductor chip 22 inadvance.

(4) Then, the second semiconductor chip 22 is electrically connected tothe wiring layer 4 on the circuit board 5 (see FIG. 11(d)). Morespecifically, each of the electrode pads disposed on the circuit formedsurface of the second semiconductor chip 22 is connected to the secondelectrode section of the wiring layer 4 with the wire 7.

(5) Thereafter, the first semiconductor chip 21, the secondsemiconductor chip 22, and the wires 7, provided on the circuit board 5,are sealed with a sealing resin 8 (see FIG. 11(e)). The method offorming the sealing resin 8 is similar to that described in the firstembodiment.

(6) Then, each of the packaging-use external terminals 10 is disposed ata location of a via hole 9 formed in the insulating substrate 3 of thecircuit board 5 (see FIG. 11(f)).

(7) Finally, a plurality of semiconductor devices produced on thecircuit board 5 are divided into pieces of semiconductor devices bycutting the insulating substrate 3 along the unnecessary part of theinsulating substrate 3 of the circuit board 5, i.e., along the outeredge of the sealing resin 8 of each semiconductor device unnecessaryparts (see FIG. 11(d)). The methods of cutting the insulating substrate3 include a punching method using a die, and an eximer laser method.

In the above-described first embodiment (and in the second embodiment),when mounting the second semiconductor chips 2 (22) on the firstsemiconductor chips 1 (21), if the first semiconductor chips 1 (21) andthe second semiconductor chips 2 (22) have different shapes, the secondsemiconductor chips 2 (22) may protrude from the first semiconductorchips 1 (21) as shown in FIG. 12(a). In this case, since the protrudedpart of the second semiconductor chip 2 (22) is of low strength, thesecond semiconductor chip 2 (22) may be possibly destroyed by shockproduced when, for example, wire-bonding the electrode pads 17 b of thesecond semiconductor chip 2 (22) to the wiring layer 4.

In order to solve the problem, as shown in FIG. 12(b), a support member19 having the same height and the same shape as the first semiconductordevice 1 (21) is fixed under the protruded part of the secondsemiconductor chip 2 (22). By reinforcing the second semiconductor chip2 (22) with the support member 19, destruction thereof can be prevented.The support member 19 is preferably made of Silicon (Si) in order toreduce generation of stress, etc. against a heat load applied during andafter manufacturing the semiconductor device with the CSP structure. Inaddition, the support member 19 has the same coefficient of linearexpansion as the second semiconductor chip 2 (22).

The above-mentioned semiconductor devices in accordance with Embodiments1 and 2 include two laminated semiconductor chips. However, the presentinvention can be arranged to include three or more laminatedsemiconductor chips. In this case, the third semiconductor chip can bemounted on the top of the two semiconductor chips with its circuitformed surface facing up and wire-bonded to the wiring layer 4.Alternatively, the third semiconductor chip can be mounted on the top ofthe two semiconductor chips with its circuit formed surface facing downthrough metal bumps by providing electrode pads for disposing the metalbumps on the circuit formed surface of the second semi conductor chip 2(22).

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A method of manufacturing a semiconductor devicecomprising: (a) forming a first adhesion layer on a back surface of afirst wafer on which no circuit is formed, a circuit being formed on afront surface of the first wafer; (b) producing separate firstsemiconductor chips from said first wafer by dicing; (c) mounting saidfirst semiconductor chip on a wiring layer with its back surface facingsaid wiring layer; (d) forming a second adhesion layer on a back surfaceof a second wafer on which no circuit is formed, a circuit being formedon a front surface of the first wafer; (e) producing separate secondsemiconductor chips from said second wafer by dicing; and (f) mountingsaid second semiconductor chip on said first semiconductor chip with itsback surface facing said first semiconductor chip.
 2. The method ofmanufacturing the semiconductor device as set forth in claim 1, furthercomprising the steps of: (g) wire-bonding an electrode section of saidfirst semiconductor chip to an electrode section of said wiring layerwith a first wire; (h) wire-bonding an electrode section of said secondsemiconductor chip to an electrode section of said wiring layer with asecond wire; and (i) sealing said first and second semiconductor chipsand said first and second wires, said steps (g) to (i) being includedafter said step(f).
 3. The method of manufacturing the semiconductordevice as set forth in claim 2, further comprising the steps of: (j)forming a metal ball on each end of said second wire; (k) connecting oneof the metal balls to the electrode section of said second semiconductorchip; (l) cutting said second wire; and (m) making a surface of themetal ball connected to said second semiconductor chip flat; said steps(j) to (m) being included between said steps (g) and (h).
 4. The methodof manufacturing the semiconductor device as set forth in claim 1,further comprising the steps of: (g) wire-bonding an electrode sectionof said first semiconductor chip to an electrode section of said wiringlayer with a first wire; (h) forming a metal ball on each end of asecond wire; (i) connecting one of the metal balls to the electrodesection of said second semiconductor chip; (j) cutting said second wire;(k) wire-bonding an electrode section of said second semiconductor chipto an electrode section of said wiring layer with said second wire; and(l) sealing said first and second semiconductor chips and said first andsecond wires.
 5. The method of manufacturing the semiconductor device asset forth in claim 1, further comprising the steps of: (g) forming ametal ball on each end of a first wire; (h) connecting one of the metalballs to an electrode section of said first semiconductor chip; (i)cutting said first wire; (j) wire-bonding the electrode section of saidfirst semiconductor chip to an electrode section of said wiring layerwith said first wire; (k) wire-bonding the electrode section of saidfirst semiconductor chip to an electrode section of said secondsemiconductor chip with a second wire; (l) sealing said first and secondsemiconductor chips and said first and second wires.
 6. The method ofmanufacturing the semiconductor device as set forth in claim 1, furthercomprising the steps of: (g) forming a metal ball on each end of a firstwire; (h) connecting one of the metal balls to a dummy pad providing onsaid first semiconductor chip; (i) cutting said first wire; (j)wire-bonding the dummy pad of said first semiconductor chip to anelectrode section of said wiring layer with said first wire; (k)wire-bonding the dummy pad of said first semiconductor chip to anelectrode section of said second semiconductor chip with a second wire;and (l) sealing said first and second semiconductor chips and said firstand second wires.
 7. A method of manufacturing a semiconductor devicecomprising: (a) forming an insulating layer and a metal bump on a wiringlayer; (b) mounting a first semiconductor chip on said wiring layer withits circuit-formed surface facing said wiring layer; (c) forming anadhesion layer on a back surface of a wafer on which no circuit isformed, whereby a circuit is formed on a front surface of the wafer; (d)producing separate second semiconductor chips from the wafer by dicing;(e) mounting said second semiconductor chip on said first semiconductorchip with the back surface of the second semiconductor chip facing saidfirst semiconductor chip; (f) wire-bonding an electrode section of saidsecond semiconductor chip to an electrode section of said wiring layerwith a wire; and (g) sealing said first and second semiconductor chipsand said wire.
 8. The method of manufacturing the semiconductor deviceas set forth in claim 7, further comprising the steps of: (h) forming ametal ball on each of said wire; (i) connecting one of the metal ballsto the electrode section of said second semiconductor chip; (j) cuttingsaid wire; and (k) making a surface of the metal ball connected to saidsecond semiconductor chip flat; said steps (h) to (k) being includingbetween said steps (e) and (f).
 9. The method of manufacturing thesemiconductor device as set forth in claim 7, further comprising thesteps of: (h) forming a metal ball on each of said wire; (i) connectingone of the metal balls to the electrode section of said secondsemiconductor chip; and (j) cutting said wire; said steps (h) to (j)being including between said steps (e) and (f).
 10. A method ofmanufacturing a semiconductor device comprising: (a) applying anadhesive paste on a wiring layer, and thereafter, mounting a firstsemiconductor chip on said wiring layer with a back surface of saidsemiconductor chip facing said wiring layer, the back surface having nocircuit formed thereon; (b) forming an adhesion layer on a back surfaceof a wafer on which no circuit is formed, whereby a circuit is formed ona front surface of the wafer; (c) producing separate secondsemiconductor chips from the wafer by dicing; and (d) mounting saidsecond semiconductor chip on said first semiconductor chip with the backsurface of the second semiconductor chip facing said first semiconductorchip.
 11. The method of manufacturing the semiconductor device as setforth in claim 10, further comprising the steps of: (e) wire-bonding anelectrode section of said first semiconductor chip to an electrodesection of said wiring layer with a first wire; (f) wire-bonding anelectrode section of said second semiconductor chip to an electrodesection of said wiring layer with a second wire; and (g) sealing saidfirst and second semiconductor chips and said wires, said steps (e) to(g) being included after said step (d).
 12. The method of manufacturingthe semiconductor device as set forth in claim 10, further comprisingthe steps of: (e) wire-bonding an electrode section of said firstsemiconductor chip to an electrode section of said wiring layer with afirst wire; (f) forming a metal ball on each end of a second wire; (g)connecting one of the metal balls to the electrode section of saidsecond semiconductor chip; and (h) cutting said second wire; (i)wire-bonding an electrode section of said wiring layer to the electrodesection of said second semiconductor chip with said second wire; (j)sealing said first and second semiconductor chips and said first andsecond wires, said steps (e) to (j) being included after said step (d).13. The method of manufacturing the semiconductor device as set forth inclaim 10, further comprising the steps of: (e) forming a metal ball oneach end of a first wire; (f) connecting one of the metal balls to theelectrode section of said first semiconductor chip; and (g) cutting saidfirst wire; (h) wire-bonding an electrode section of said wiring layerto the electrode section of said first semiconductor chip with saidfirst wire; (i) wire-bonding the electrode section of said firstsemiconductor chip to an electrode section of said second semiconductorchip with a second wire; (j) sealing said first and second semiconductorchips and said first and second wires, said steps (e) to (j) beingincluded after said step (d).
 14. The method of manufacturing thesemiconductor device as set forth in claim 10, further comprising thesteps of: (e) forming a metal ball on each end of a first wire; (f)connecting one of the metal balls to a dummy pad providing on said firstsemiconductor chip; (g) cutting said first wire; (h) wire-bonding thedummy pad of said first semiconductor chip to an electrode section ofsaid wiring layer with said first wire; (i) wire-bonding the dummy padof said first semiconductor chip to an electrode section of said secondsemiconductor chip with a second wire; and (j) sealing said first andsecond semiconductor chips and said first and second wires, said steps(e) to (j) being included after said step (d).
 15. A method ofmanufacturing a semiconductor device comprising: (a) forming a firstadhesion layer on a back surface of a first wafer, no circuit beingformed on the back surface of the first wafer; (b) producing separatefirst semiconductor chips from said first wafer by dicing; (c) mountingat least one of said first semiconductor chips on a wiring layer withthe back surface of the at least one first semiconductor chip facingsaid wiring layer; (d) forming a second adhesion layer on a back surfaceof a second wafer, no circuit being formed on the back surface of thesecond wafer; (e) producing separate second semiconductor chips fromsaid second wafer by dicing; and (f) mounting at least one of saidsecond semiconductor chips on said at least one of said firstsemiconductor chip with the back surface of the at least one secondsemiconductor chip facing said at least one of said first semiconductorchips.